The present invention relates to a magnetic tape scanning assembly for use in a video tape recorder and playback apparatus, and more particularly to a magnetic tape scanning assembly having a guiding path that has desirable surface characteristics.
U.S. Pat. No. 3,955,215 discloses apparatus and method for forming a head drum assembly for a video tape recorder and playback apparatus in which a rotatable magnetic head assembly is interposed between a pair of stationary drums. A pair of magnetic heads fixed to the head assembly are protruded from the peripheries of the drums so that a magnetic tape which passes a guiding path diagonally formed on the peripleries of the drums is magnetically scanned with the magnetic heads as the magnetic tape travel with guiding path. Although various types of loading and unloading mechanisms and systems are known and disclosed as in U.S. Pat. No. 3,979,772, and U.S. Pat. No. 3,333,753, explanations about tape loading and unloading mechanisms and systems are omitted from the specification for simplicity, as such the explanations are not concerned with the present invention.
U.S. Pat. No. 3,333,753 discloses another type of a magnetic tape scanning assembly in which a rotatable drum having a pair of magnetic heads is supported on a shaft, and a stationary drum is coaxially supported about the shaft. A diagonal or helical guiding path is formed on the peripheries of the drums. These two types of magnetic tape scanning assemblies are on practical use.
In the conventional magnetic tape scanning assemblies, guiding means including a cyindrical stationary drum and a rotatable magnetic head assembly are of extreme importance. As a magnetic tape under tension slides the guiding path formed on the stationary drum, the drum must have a small coefficient of sliding friction and a good wear resistance. If a coefficient of sliding friction is large, jitters may appear on the screen of a cathode ray tube. Further, if wear resistance is poor, the surface of the guiding path will become like a mirror surface resulting that the magnetic tape is adsorbed and sticked on such the surface of the guiding path. Such the adsorption of the magnetic tape will make the scanning assembly inoperable.
In order to make small a cofficient of sliding friction of the guiding path of the drums which have heretofore been made of aluminum material or aluminum-silicon alloy material, various measures have been employed one of which was surface treatment with, such as, ceramic coating, alumite coating, metal plating, etc. These conventional surface treatments were not staisfied in wear resistance and coefficient of sliding friction and were expensive because of an increase in manufacturing steps.
As a demand for high quality magnetic tapes with highly smoothed surfaces increases, the requirements i,e, low coefficient of sliding friction and wear resistance are becoming severer and severer. In recent color video tape recorder and playback apparatus, the following characteristics are required for magnetic tape guiding assemblies.
(1) Small coefficient of sliding friction--less than 0.3 when measured under a sliding test which will be described hereinafter. PA1 (2) Good wear resistance--a wear amount (.mu.m) in terms of decrease in peak height of the guiding path is less than 0.7 when measured under a wear test which will be described hereinafter. PA1 (3) Magnetic tape surface is not injured by scraching with the guiding path. PA1 (4) Good surface condition of the guiding path--the surface should maintain a good surface condition for a long period of time.